1. Field of the Invention
The present invention relates to an image pickup device or image sensor, and more particularly, to an image pickup device comprising a plurality of electron-emitting devices arranged in, for example, a two-dimensional matrix.
2. Description of the Related Art
Electron-emitting devices in which electrons are drawn out by an electric field without the need of cathode heating are used as electron sources of field emission displays (FED). For example, according to the light emission principle of an FED having a pyramid-shaped Spindt-type cathodes, the light emission is achieved by drawing electrons out to a vacuum by a gate electrode disposed apart from a cathode, and having those electrons collided with a phosphor applied on a transparent anode in the same manner as a CRT (cathode ray tube) although there is a difference as the FED employs the cold cathode.
The use of cold cathode electron-emitting devices in an image pickup device has been proposed. For example, a vidicon electron tube device with increased emission efficiency by arranging a plurality of cathodes as described in JP-A-4-312752 is known.
However, this minute Spindt-type field emission source has a problem of low manufacturing production since it requires a large number of complicated manufacturing processes for the cold cathodes.
Also known is an image pickup device as disclosed in JP-A-5-6749, in which a plurality of cold cathodes of surface electron sources are arranged in a matrix to cause emitted electrons to be incident on a photoconductive film located in an imaging plane. As for the surface electron sources, electron-emitting devices having a metal-insulator-metal (MIM) structure are used.
However, the amount of electron emission is not sufficient even with the use of such MIM-type electron-emitting devices.
An object of the present invention, which was invented in consideration of the above conditions, is to provide an image pickup device using electron-emitting devices that are capable of providing stable electron emission with a low voltage.
An image pickup device of the present invention comprises a pair of first and second substrates facing each other with a vacuum space therebetween; and a plurality of electron-emitting devices provided on the first substrate and a photoconductive film provided on the second substrate, the electron-emitting devices each comprising an insulating layer deposited over an electron source layer which is, in turn, formed over an ohmic electrode, and a metal thin film electrode deposited over the insulating layer, the insulating layer and the metal thin film electrode having electron-emitting sections as island regions in which their film thicknesses are gradually reduced toward the electron source layer.
In the image pickup device according to one aspect of the invention, said insulating layer is made of a dielectric material and has a film thickness of 50 nm or greater in an area other than said island region.
In the image pickup device according to one aspect of the invention, said metal thin film electrode terminates over said insulating layer within said island region.
In the image pickup device according to one aspect of the invention, said insulating layer terminates over said electron source layer within said island region.
In the image pickup device according to one aspect of the invention, said island region is a recess on a flat surface of said metal thin film electrode.
In the image pickup device according to one aspect of the invention, said insulating layer and said metal thin film electrode are deposited by one of a physical deposition method and a chemical deposition method.
In the image pickup device according to one aspect of the invention, bus lines are formed over a plurality of said metal thin film electrodes, said ohmic electrodes and said bus lines being stripe-shaped electrodes arranged in directions orthogonal to each other.
In the image pickup device according to one aspect of the invention, the device further comprises a reverse-tapered block within each of said island regions.
According to the present invention having the above configuration, within the island-like portions of the insulating layer and the metal thin film electrode, their film thicknesses are gradually reduced toward the electron source layer in a direction their interface lays, resulting in an increased amount of electrons emitted from those island regions, and since such electron-emitting devices are used for an image pickup device, miniaturization of the device can be achieved. In addition, since the emitted electrons exhibit favorable recticlinearlity, output signals (video signals) of high resolution may be obtained.
Furthermore, according to an image pickup device of the present invention, since the insulating layers of the electron-emitting devices have a large film thickness, through-hole are unlikely to occur so that the manufacturing yield would be improved.